Filter element

ABSTRACT

The invention relates to a filter element ( 3 ) designed as a replacement element, of which the filter medium ( 59 ), which is formed as a hollow body and extends between two closure parts, in particular in the form of end caps ( 13, 19 ), is pleated with individual filter folds ( 66 ), characterized in that the filter medium ( 59 ) comprises a filter material ( 61 ) made of cellulose.

The invention relates to a filter element designed as a replacement element, of which the filter medium, which is formed as a hollow body and extends between two closure parts, in particular in the form of end caps, is pleated with individual filter folds. The invention further relates to a device for replaceably receiving such a filter element and to a method for producing a filter medium made of cellulose for such a filter element.

Filter elements of this type are prior art. Such filter elements are widely used in hydraulic systems of diverse designs in order to ensure the operational reliability of the systems concerned by removing contaminating foreign substances from the hydraulic fluid. Such filter elements are also used advantageously in fuel supply systems. For example, DE 10 2011 119 868 A1 discloses a filter device for fluids such as diesel fuel that are contaminated with water admixtures, said device having a filter element through which the fluid concerned can flow from the dirty side to the clean side in a filter housing and which, for multiphase filtration and water separation, has at least one filter material that mainly separates water and a filter material that mainly retains particulate contaminants, wherein a water collector is present for receiving the separated water and wherein a coalescing filter medium serves as the filter material that mainly separates water.

However, fluids such as hydraulic fluids frequently also have emulsified water constituents, which need to be separated out, at least partially, during filtration. Typical filter elements of prior art design frequently do not adequately fulfill this requirement.

With respect to these problems, the invention is based on the object of providing a filter element which enables a particularly effective separation of water in the filtering of fluids with an oil-water emulsion, which operates in a functionally reliable manner, and which can be produced economically.

According to the invention, this object is achieved with a filter element having the features of claim 1 in its entirety.

According to the characterizing part of claim 1, an essential feature of the invention lies in the fact that the filter element has a filter material made of cellulose. As the fluid flows through, the cellulose fibers exert a coalescing effect, thus causing enlarged droplets to form from the aqueous fraction of the emulsion. Owing to the difference in density of water and oil, these droplets descend and are thus separated from the less dense medium. In practical tests, it turned out that such a filter element performs said water separation in a functionally reliable manner and is furthermore economical to produce. Owing to the pleating of the filter medium with the resulting formation of individual filter folds, the filter surface area is significantly increased such that said separation is induced in a particularly effective and consequently highly efficient manner. There is not any counterpart to this in the prior art.

The pleated filter medium, which forms the hollow body, is preferably firmly connected on its two adjacent, mutually facing longitudinal edges by a weld and/or an adhesive bond. The lateral geometry is permanently secured by the firm connection.

In particularly advantageous exemplary embodiments, the cellulose filter medium with a uniform thickness of more than 2 mm has equally high filter folds, which are provided with equal bend or fold radii in the valleys and peaks and which merge into one another in one piece, omitting the weld and/or adhesive bond. A powerful coalescing effect, which in turn enables a particularly effective water separation, is achievable with this uniform thickness and the uniform fold geometry.

Advantageously, it can be arranged such that the bend radii in the valleys and peaks of all folds are equal and that the filter medium shaped into the hollow body delimits fluid spaces tapering towards each other with individual filter folds. The succession of the fluid spaces thus formed ensures an incident flow onto the greatest possible exposed filter surface area of the cellulose material.

The cellulose filter medium can be used in a particularly advantageous manner for separating water from hydraulic fluids, wherein the filter medium enlarges the water droplets in the water-oil mixture in terms of volume. Owing to the difference in density between water and oil, the water droplets descend under the effect of gravity, wherein a separation process takes place under the influence of gravity.

In particularly advantageous exemplary embodiments, the cellulose filter medium is provided with at least one protective layer, such as a non-woven or woven fabric, on at least one of its sides, such as the filtrate side and the unfiltrate side. This protective layer follows the contour of the folds. The cellulose material is thus protected on both sides from damage. A protective fabric can advantageously be a fine metal mesh such as the one provided with a so-called mesh pack in prior art filter elements.

In a particularly advantageous manner, it can be arranged such that the cellulose filter medium is enveloped by a particle filter. This particle filter can function as a prefilter during the filtration process.

For this purpose, it can be advantageously arranged such that the particle filter has a further pleated filter medium, of which the filter folds have a greater packing density and possess a greater fold height than the filter folds of the filter medium made of cellulose material. The particle filter can be made out of several material layers in the manner typical for such filter media.

In advantageous exemplary embodiments, a fluid-permeable support tube is arranged between both filter media, and a further support tube is preferably arranged on the side of the cellulose filter facing away from the first support tube. Support tubes extending between the end caps increase the stability of the construction unit of the filter element.

In advantageous fashion, the two opposite end caps, as closure parts, can receive the two hollow bodies configured as hollow cylinders of both filter media between themselves, wherein the particle filter preferably envelops the cellulose filter on the downstream side thereof.

Also subject matter of the invention is a device for replaceably receiving a filter element according to any one of claims 1 to 10, said device having the features of claim 11 in its entirety. Accordingly, the device has a filter housing with a receiving chamber for the filter element with several fluid connection points, and the device is characterized in that the receiving chamber is at least partially traversed by a receiving rod, on which the filter element can be centrally positioned, which can be secured on the rod by one of its end caps and an additional securing mechanism. A space-saving design of the filter housing is possible because provision is made of a central holding mechanism with a centrally located inner holding rod and an associated securing mechanism for the filter element, and consequently there are no mechanisms for holding the filter element that project past the outer circumference of the filter element.

Advantageously, it can be arranged such that, in the state in which the filter element is installed on the receiving rod in the housing, each end cap is mounted via a spacer with a sealing function on both the securing mechanism and an intermediate bottom of the housing. The securing mechanism thus assumes the additional sealing of the filtrate side in the filter housing.

In the case of a flow through the filter element from outside to inside or from inside to outside, the intermediate bottom together with the filter element can separate a water collection chamber with oil and water fluid connection points on the clean side from an unfiltrate chamber, which has a fluid connection point for supplying the oil-water mixture on the unfiltrate side of the filter element.

Advantageously, the housing can be designed as a part for installation in a fluid tank and closed to the environment by means of a removable housing lid.

According to claim 15, also subject matter of the invention is a method for producing a cellulose filter medium for a filter element according to any one of claims 1 to 10, said method comprising at least the following production steps:

-   -   Moistening a flat filter pad made of cellulose material,     -   Pleating the moistened filter pad by means of a pleating         machine,     -   Forming a preferably cylindrical hollow body,     -   Joining both longitudinal sides of the hollow body by means of a         welding and/or bonding process, and     -   Drying the cellulose filter medium.

According to claim 16, the following supplementary production steps are provided for the method:

-   -   Applying a layer, preferably made of non-woven or woven fabric,         to one side, preferably both sides, of the flat cellulose filter         pad, and     -   Pleating each further layer together with the filter pad by         means of the pleating machine.

The invention is explained in detail below, with reference to exemplary embodiments illustrated in the drawings, wherein:

FIG. 1 shows a longitudinal section of an exemplary embodiment of the device according to the invention, which is provided for receiving a filter element according to the invention;

FIG. 2 shows a longitudinal section of a modified exemplary embodiment of the device according to the invention;

FIG. 3 shows a longitudinal section of the filter element, illustrated separately, according to an exemplary embodiment of the invention;

FIG. 4 shows a horizontal section of the exemplary embodiment of the filter element;

FIG. 5 shows a magnified portion of he circled area designated by V in FIG. 4; and

FIG. 6 shows a cut-off and schematically simplified oblique perspective view of a part of a pleating mechanism for producing the cellulose filter medium according to the production method of the invention.

A filter housing, which is provided for receiving a filter element 3 according to an exemplary embodiment of the invention, is designated as a whole by 1 in FIGS. 1 and 2. The filter housing 1 has a main part 5 in the shape of a hollow cylinder, which is closed on the bottom end in the figures by a bottom part 7, which is welded to the main part 5. On the top end, the filter housing 1 is closed by a housing lid 9, which can be taken off for installing and removing the filter element 3. When installing the filter device in a fluid tank, for example in a storage tank for hydraulic fluid, the housing lid 9 can form the closure for a tank opening. An intermediate bottom 11, on which the filter element inserted in the receiving chamber is mounted with its bottom closure part, is formed in the receiving chamber by the bottom part 7. This bottom closure part is formed by a typical plastic end cap 13, which has a central opening 15 as an access to the inner filter cavity 17 of the filter element 3. A top end cap 19 corresponding to the bottom end cap 13, which also possesses a central opening 21, is provided as a top closure part.

In the exemplary embodiment illustrated in FIG. 1, which provides for a flow through the filter element 3 from the outside thereof to the inner filter cavity 17, the intermediate bottom 11 possesses a flat wall 23 as a bearing surface for the filter element 3, which wall extends uninterruptedly from outer circumference to outer circumference and which has a central passage opening 25 that aligns with the opening 15 of the superimposed filter element 3. The bottom end cap 13 is mounted on the wall 23 via a sealing element forming a spacer 27. For the sealing function, the spacer 27 can be made of an elastomer or metallic sealing element. On the bearing surface for the spacer 27, the wall 23 of the intermediate bottom 11 has a slightly projecting, circumferential annular rib 29, which forms a sealing edge with the spacer 27.

For securing the filter element 3 on the mounting on the intermediate bottom 11, a receiving rod 31 is provided, which extends coaxially to the longitudinal housing axis 33 through the inner filter cavity 17 of the superimposed filter element 3, starting from the floor of the bottom part 7. To form a securing mechanism, a clamping plate 35 is mounted slidably on the top end region of the receiving rod 31 and sealed with respect to the rod 31 by a sealing ring 37. The clamping plate 35 overlapping the top end cap 19 can be pressed against the filter element 3 by a nut 39 seated on a male thread of the rod 31, wherein, in a manner analogous to the holder formed on the bottom end cap 13, a spacer 27 with a sealing function is inserted between the clamping plate 35 and the end cap 19 and the clamping plate 35, for improving the seal, also has a projecting circumferential annular rib 29 that forms a sealing edge. In the exemplary embodiment of FIG. 1, which provides for a flow through the filter element 3 from the outside to the inside, a fluid connection point 41 for supplying an oil-water emulsion as unfiltrate is situated on the housing lid 9. A connection point 45 is provided on the bottom part 7 for the outflow of the oil as filtrate from the chamber 43 of the bottom part, which connection point is situated in proximity to the top wall 23. A further connection point 47 is situated on the floor of the chamber 23, and thus on the bottom, as an outlet for separated water.

In the example of FIG. 2, which provides for a flow through the filter element 3 from the inner filter cavity 17 to the outside, the design of the intermediate bottom 11 is modified with respect to FIG. 1, the design of the fixation of the filter element 3 by means of the securing mechanism otherwise remaining the same. Instead of the flat, uninterrupted wall 23 of FIG. 1, the intermediate bottom 11 forms an outer circular disc 49, on the radially inner end of which is attached an upwardly projecting annular body 51, which with its top end face forms the bearing for the bottom end cap 13 of the filter element 3, wherein, as in FIG. 1, a spacer 27 with a sealing function is positioned on the bearing surface and a projecting annular rib 29 is provided as a sealing edge on the bearing surface of the annular body 51. In this form of the intermediate bottom 11, the connection point 41 for the oil-water emulsion is situated on the floor of the chamber 44, which is connected to the inner filter cavity 17. The chamber 53 surrounding the annular body 51, which is connected to the filtrate side 55 on the outside of the filter element 3, forms a water collection chamber on which the connection point 47 for the outflow of separated water is situated. In this case the connection point 45 for discharging the oil as filtrate is provided in a central location on the lid 9.

Details of the filter element 3 are shown more clearly in FIGS. 3 to 5. The filter medium situated between the end caps 13, 19 has a cellulose filter material 59, which consists of a pleated filter pad 61 (FIG. 6) which is shaped into a circular cylindrical hollow body. The hollow body is closed at the joint by a bonded or welded lengthwise seam. According to the method of the invention, the cellulose filter material 59 is pleated from a filter pad 61 with a uniform thickness of more than 2 mm in such a way that equally high filter folds are formed, which have equal bend or fold radii in the valleys and peaks. A fluid-permeable support tube 63 extending from end cap to end cap abuts on the inside of the hollow body of the cellulose filter material 59, which also extends between the end caps 13 and 15. As is most readily discernible in FIG. 3, a support ring 65, which holds the support tube 63 in contact with the inside of the cellulose filter material 59, abuts the inside of each end cap 13 and 19. As the enlarged portion depicted in FIG. 5 shows, tapered fluid spaces 67 are formed between the individual folds 66 in the filter material 59 folded with the same inner and outer bend radii. As a result, not only are surface areas of the filter material 59 exposed as effective filter surface, but also free spaces are formed for descending water droplets, which will be explained in more detail below.

On the outside, the cellulose filter material 59 is enveloped by a particle filter 69, which, like the cellulose filter material 59, is arranged as a circular cylindrical hollow body between the end caps 13 and 19. The particle filter 69 is made in the usual manner from several pleated layers in the nature of a so-called mesh pack. Situated between the particle filter 69 and the cellulose filter material 59 is a further fluid-permeable support tube 71, which extends from the bottom end cap 13 to the top end cap 19.

FIG. 6 shows a simplified schematic of the production of the pleated filter pad 61 which forms the filter material 59 according to the method of the invention. As shown, a web 75 of the more than 2 mm thick cellulose material is moved through in the direction indicated by the arrow 77 under a spray bar 79, which moistens the still flat web 75, bringing it into a softened state suitable for a pleating process. The web 75 then runs through a pleating machine of typical design, which carries out the pleating process using moveable pleating knives 81 and 83, thus forming the pleated filter pad 61. After the formation of the hollow body that forms the cellulose filter material 59, this hollow body is then closed by connecting its two longitudinal sides by means of a welding and/or bonding process, after which the cellulose filter material 59, when dry, is installed in the filter element 3. Before carrying out the pleating process, a layer forming a protective cover, which is preferably composed of a non-woven or woven fabric such as a fine metal mesh, is applied on one side, preferably on both sides, of the still flat web 75 and pleated together with the respective other layers by means of the pleating machine.

In the filtration mode, in the example of the device shown in FIG. 1, there is a flow through the filter element 3 from the outside of the particle filter 69 into the inner filter cavity 17. Accordingly, the connection point 41 forms the inlet for the unfiltrate, which is in the form of an oil-water emulsion. During the throughflow, the cellulose material of the cellulose filter material 59 acts as a coalescing medium so that enlarged droplets are formed from the water content of the emulsion. These droplets descend along the support tube 63 and descend via the openings 15 of the end cap and 25 in the wall 23 of the intermediate bottom 11 into the chamber 43, which thus forms a water collection chamber. In this case the connection point 47 situated on the floor of the chamber 43 forms the outlet for separated water. The connection point 45 forms the filtrate outlet for the filtrate, which likewise flows from the inner filter cavity 17 into the chamber 43 via the openings 15 and 21. Because the connection point 45 is arranged in the top end region of the chamber 43, it is situated at a level above the dividing line formed by the oil/water density difference.

In the exemplary embodiment of FIG. 2, in the operating mode there is a flow through the filter element 3 from the inner filter cavity 17 thereof to the outside. Accordingly, the connection point 41 to the chamber 44 below the intermediate bottom 11 forms the inlet for the oil-water emulsion, which flows via the opening 25 between the annular body 51 into the filter cavity 17. The water droplets formed by coalescence as the emulsion flows through the cellulose fiber material 59, which descend along the downstream-side support tube 71, arrive with the given direction of flow at the filtrate side 55, which transitions at the bottom end cap 13 into the chamber 53, which is delimited by the intermediate bottom 11 and the outside of the annular body 51 of the bottom part 7. This chamber 53 thus forms the water collection chamber, from which the separated water flows out via the connection point 47 situated on the chamber 53. The oil flows out as filtrate via the connection point 45 on the housing lid 9, which forms the top closure of the filtrate side 55. 

1. A filter element (3) designed as a replacement element, of which the filter medium (59), which is formed as a hollow body and extends between two closure parts, in particular in the form of end caps (13, 19), is pleated with individual filter folds (66), is characterized in that the filter medium (59) has a filter material (61) made of cellulose.
 2. The filter element according to claim 1, characterized in that the pleated filter medium (59), which forms the hollow body, is firmly connected at its two adjacent, mutually facing longitudinal edges by a weld and/or an adhesive bond.
 3. The filter element according to claim 1, characterized in that the filter material (61) composed of cellulose with a uniform thickness of more than 2 mm has equally high filter folds (66), which, provided with equal bend or fold radii in the valleys and peaks, merge into one another in one piece, omitting the weld and/or adhesive bond.
 4. The filter element according to claim 1, characterized in that the bend radii in the valleys and peaks of all folds (66) are equal and that the filter material (61) formed into the hollow body delimits, with individual filter folds (66), fluid spaces (67) tapering toward one another.
 5. The filter element according to claim 1, characterized in that the filter medium (59) composed of cellulose is used to separate water from hydraulic fluids and increases water droplets in the water-oil mixture in terms of volume, which droplets descend under the effect of gravity owing to the difference in density between water and oil.
 6. The filter element according to claim 1, characterized in that the filter medium (59) composed of cellulose is provided, at least on one of its sides such as the filtrate side and the unfiltrate side, with at least one protective layer such as a non-woven or woven fabric, which follows the contour of the folds.
 7. The filter element according to claim 1, characterized in that the filter medium (59) composed of cellulose is enveloped by a particle filter (69).
 8. The filter element according to claim 1, characterized in that the particle filter (69) has a further pleated filter medium, of which the filter folds have a greater packing density and possess a greater fold height than the filter folds (66) of the filter medium (59) made of cellulose material.
 9. The filter element according to claim 1, characterized in that a fluid-permeable support tube (71) is arranged between both filter media (59, 69), and that a further support tube (63) is preferably arranged on the side of the cellulose filter medium (59) facing away from the support tube (71).
 10. The filter element according to claim 1, characterized in that the two opposite end caps (13, 19), as closure parts, receive the two hollow bodies of the two filter media (59, 69) configured as hollow cylinders between themselves, and that the particle filter (69) envelops the cellulose filter (59), preferably on the downstream side thereof.
 11. A device for replaceably receiving a filter element (3) according to claim 1, having a filter housing (1), which has a receiving chamber for the filter element (3) with several fluid connection points (41, 45, 47), characterized in that the receiving chamber is at least partially traversed by a receiving rod (31) on which the filter element (3) can be centrally positioned, which can be secured on the rod (31) by one of its end caps (19) and an additional securing mechanism (35, 39).
 12. The device according to claim 11, characterized in that, in the state in which the filter element (3) is installed on the receiving rod (31) in the housing (1), each end cap (13, 19) is mounted via a spacer (27) with a sealing function on the securing mechanism (35, 39) and on an intermediate bottom (11) of the housing (1).
 13. The device according to claim 11, characterized in that, with a flow through the filter element (3) from the outside to the inside or from the inside to the outside, the intermediate bottom (11) together with the filter element (3) separates a water collection chamber (43, 53) with oil and water fluid connection points (45, 47) on the clean side from an unfiltrate chamber with a fluid connection point (41, 47) for supplying the oil-water mixture on the unfiltrate side of the filter element (3).
 14. The device according to claim 11, characterized in that the housing (1) is designed as a part for installation in a fluid tank and is sealed with respect to the environment by means of a removable housing lid (9).
 15. A method for producing a filter medium (59) made of cellulose for a filter element (3) according to claim 1, having at least the following production steps: Moistening a flat filter pad (75) made of cellulose material, Pleating the moistened filter pad by means of a pleating machine (81, 83), Forming a preferably cylindrical hollow body, Joining the two longitudinal sides of the hollow body by means of a welding and/or bonding process, and Drying the filter medium (59) made of cellulose.
 16. The method according to claim 15, characterized in that it is supplemented by the following production steps: Applying a layer, preferably made of non-woven or woven fabric, to one, preferably both sides of the flat cellulose filter pad (75) and Pleating each further layer together with the filter pad (75) by means of the pleating machine (81, 83). 